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Intro to Telecom

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Title: Intro to Telecom


1
Intro to Telecom
2
Fig 6.2
3
Analog and Digital Signals
Digital signal
Analog signal
Fig. 6.4
  • Analog
  • Continuous fluctuations over time between high
    and low voltage
  • Digital
  • A discrete voltage state

4
Fig 6.3
5
Source/Signal Combinations
6
Basic Modulation Techniques
  • Amplitude modulation (AM)
  • Converts digital data to analog signals using a
    single frequency carrier signal
  • High-amplitude wave denotes a binary 1
  • Low-amplitude wave denotes a binary 0
  • Frequency modulation (FM)
  • Uses a constant amplitude carrier signal and two
    frequencies to distinguish between 1 and 0
  • Phase modulation
  • Uses a phase shift at transition points in the
    carrier frequency to represent 1 or 0

7
Examples Analog shifts
8
Data Transmission Speeds
  • Measured in bits per second (bps)
  • Kilobits per second (kbps)
  • Megabits per second (Mbps)
  • Gigabits per second (Gbps)

9
Types of Communications Media
  • Guided Media
  • Twisted wire cable
  • Coaxial cable
  • Fiber-optic cable
  • Unguided Media
  • Microwave transmission - satellite
  • Microwave transmission - terrestrial
  • Cellular transmission
  • Infrared transmission

10
Cable/Wire Types
  • Twisted Pair Wire
  • A cable consisting of pairs of twisted wires
  • The twist helps the signal from bleeding into
    the next pair
  • Cheapest
  • Limited bandwidth
  • Coaxial Cable
  • Inner conductor wire surrounded by insulation,
    called the dielectric
  • Dielectric is surrounded by a conductive shield,
    which is in turn covered by a layer of
    nonconductive insulation, called the jacket
  • More expensive than twisted pair, but higher
    bandwidth

11
Twisted Pair
  • Fig 6.4

12
Coaxial Cable
  • Fig 6.5

13
Cable/Wire Types, Continued
  • Fiber Optic Cable
  • Consists of many extremely thin strands of solid
    glass or plastic bound together in a sheathing
  • Transmits signals with light beams
  • No risk of sparks, safe for explosive
    environments
  • More expensive than coaxial, but more bandwidth
  • Different colors of light are used to
    simultaneously send
  • Multiple signals

14
Fiber Optic Cable
  • Fig 6.6

15
Microwave Transmission
  • Fig 6.7

16
Satellite
  • Fig 6.8

17
Cellular
  • Fig 6.9

18
Table 6.1
19
Communications Efficiency
  • A large part of telecommunication expense is cost
    of the medium
  • Several approaches are used to efficiently use
    the medium
  • Multiplexing
  • Switching
  • Compressing

20
Multiplexing Time Division and Frequency
Division
Figure 6.14
Time division multiplexing (TDM) is where
multiple incoming signals are sliced into small
time intervals
Frequency division multiplexing (FDM) is where
incoming signals are placed on different
frequency ranges
21
Multiplexing Freeway Analogy
  • Frequency division multiplexing is analogous to
    having a 3-lane freeway. Each car has its own
    lane, three cars drive simultaneously in the same
    direction.
  • Time division multiplexing is analogous to a
    freeway-onramp cars enter the on-ramp one at a
    time, and drive in single file.

22
Frequency Division of Cable
Base video width is 4.2 MHz with guard bands 6 MHz
.....
Ch n
Ch 1
Ch 2
Ch 3
Ch 4
Ch 5
Ch 6
The default is 6 Mega Hertz slices of bandwidth
per channel
Cable modem
--Cable Bandwidth--
Cable phone gets 4 KHz slices
Q What limits the bandwidth on coaxial cable?
A The bandwidth of the amplifier.
23
Switching
  • Switching further advances the objective of
    efficiently utilizing the circuit
  • Two types
  • Circuit switching (e.g., public telephone
    network) requires end-to-end physical connection
  • Packet switching (e.g. Internet) breaks up
    messages into small packets and routes them
    individually. No end-to-end physical connection
    required. Can be virtual circuit (all packets
    travel through same route) or datagram (packets
    may travel through any route)

24
Circuit Switching
medium
You
Switch
To communicate a physical connection must be made
and maintained
Your Mom
25
Packet Switching
Packets thrown into the internet cloud either
independently find the path from point to point
(datagram) of follow the same path (virtual
circuit)
26
The message
Header
Message contents
Trailer
Direction of transmission
Block Check Character
Start of Header
Start of Text
End of Text
SOH
(STX)
(ETX)
BCC
If variable length header used
If variable length message used
27
A Simple Protocol Stack
Application Protocol
Application
Application
Transport Protocol
Transport
Transport
Network Access
Network Protocol
Network Access
28
A Simple Protocol Stack, Continued
  • The application uses the protocol for its
    layer/level to determine how it should format its
    message for an application at a different
    computer
  • However, it does not worry about getting the
    message to the application
  • The transport layer is responsible for making
    sure that the message arrives at the correct
    application at the correct computer
  • However, it does not concern itself with how it
    gets there. That is the responsibility of the
    network layer. The transport layer is only
    concerned with reliability of the communication
  • The network layer determines how the message
    should be presented to the network

29
Formatting and Decoding a Message
Protocols strip header information from the
message
Protocols add header information to the message
Application
Application
Data
Transport
Transport
Transport Header
Network Access
Network Access
Network Header
30
Communications Protocols
  • Fig 6.22

31
Relationship of TCP/IP to OSI
TCP/IP
  • Controls the users interface and applications
    between two hosts, e.g.
  • File transfer protocol (ftp)
  • HTTP (Hypertext trans. protocol)
  • Telnet
  • SMTP (Simple mail transfer protocol)
  • SNMP (Simple Network Mgt protocl)
  • NNTP (Net news transport protocol)

Process / Application
Host to Host
TCP Virtual circuit maintained, ack UPD No
acknowledgment
Internet
IP routing, fragmentation, assembly ICMP Above
IP, error handling ARP Address resolution sw to
hw addr RARP hardware to sw address convert
Network Access
Physical layer, such as Ethernet or Token Ring
32
Fig 6.23
33
Ethernet Evolution
New, taking over
1000 Mbps Gigabit Ethernet
Predominant
100 Mbps Ethernet
Battling ATM
Legacy
Most new installations
10 Mbps Ethernet
Old installations
34
Ethernet Pros and Cons
  • Operates by contention packets collide
  • Inefficient many aborted transmissions
  • Rates of only 37 of raw wire speed
  • 10 Gbit Ethernet on the way
  • Inexpensive
  • Simple circuitry
  • Cheapest bandwidth ratios

35
Token Ring
T
data
40008065402
T
data
36
Token Ring Pros and Cons
  • Very efficient 75 of raw bandwidth
  • A better technology
  • Expensive
  • Used for mission critical applications like
    banking
  • Lost battle to fast-Ethernet (like beta vs. VHS)

37
ATM
  • Sends 53-byte cells not variable length packets
    like Token Ring and Ethernet
  • Hardware knows where header ends and data begins
  • Speeds up to 622 Mbps
  • Predictable throughput rates very reliable,
    guaranteed service
  • Military, Safety valve in nuclear power reactor.
    No Delay or Jitter!!!

Header
Body
38
ATM Pros and Cons
  • Very fast
  • Reliable mission critical applications
  • Efficient bandwidth gt75 of raw capacity
  • No delays or sequence re-configuring
  • Very expensive and complex
  • Not compatible with 10/100 Mbps Ethernet
    installations
  • Most applications do need this efficient
    management of data cells only messages used in
    real time need ATM

Header
Body
39
Connectivity
Type Bandwidth Users Rel.Cost Modem 28.kbps 1
-5 1 DSL 256 Kbps 1-50 2 ISDN 128
Kbps 5-50 3 T1 (DS1) 1.54 Mbps 50-500 10 T3
(DS3) 45 Mbps 4000 100 ATM 155-622
Mbps 10,000 200
40
Synchronous Optical Network (SONET)
Define Optical Carrier Levels (OC) Basic
transmission rate STS-1 51.84 Mbps OC-3 351.84
Mbps 155.52 Mbps OC-12 12 51.84 Mbps
622.08 Mbps OC-48 2.488 Gbps OC-768 ?????
41
Bringing in the fiber
  • 48 strands - OC 48
  • 96 strands - OC 96
  • Dense Wave Division Multiplexing 48 strands can
    yield OC 192
  • Optical Switches do not convert from light to
    electricity and back to light. 100 light.

42
Current Status Fiber
  • Massive investments by telecoms in 1990s.
  • Current fiber utilization at 2.5!!!!
  • Mostly between major corporate infrastructures in
    major cities. CO to CO
  • Limitations on last mile to smaller
    infrastructures
  • Abundance trickled to equipment manufacturers as
    well predicted to last through 2002

43
Brief History of Telecom
  • 1837 - Invention of the telegraph
  • 1876 - Alexander Graham Bell invents the
    telephone
  • 1876 - Edison invents the electric bulb and the
    phonograph
  • 1880 - American Bell founded
  • 1892 - Telephone system regulation begins in
    Canada
  • 1893 - Broadcasting was started in Budapest.
  • 1906 - Lee de Forest invents the vacuum tube.
  • 1910 - Interstate Commerce Commission starts to
    regulate telcos
  • 1914 - Underground cables link Boston, NYC and
    Washington
  • 1925 - Bell Telephone Laboratories founded
  • 1930 - ATT introduces much higher quality
    insulated wire
  • 1934 - Federal Communications Commission (FCC)
    founded
  • 1945 - ATT lays 2000 miles of coax cable
  • 1952 - The first database was implemented on
    RCA's Bizmac computer
  • 1954 - Gene Amdahl developed the first computer
    operating system for the IBM 704.
  • 1968 - Carterfone court decision permits non-Bell
    telephone equipment to be used
  • 1970 - Court permits MCI to provide long-distance
    services
  • 1984 - Breakup of ATT 1984 - Cellular phones
    enter service
  • 1996 - Telecommunications Act of 1996 deregulates
    U.S. telephone system
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